Object-Oriented Terms

Classes :

A class defines the variables contained in an object, and the operations applied when the object receives a message. Every object is an instance of a class and responds to messages of that class. Each object, however, has its own copy of the variables specified in the class definition. New objects are created In Clipper language by a calling a special function that begins with the class name followed by the New suffix.

See Also: Instance Variables, Messages, Methods, Objects

Exported Instance Variables :

See : Instance Variables

Instance Variables :

Instance variables are the attributes or the data portion of an object as defined by the object’s class. Each object, when created, is given its own unique set of instance variables initialized to their default values. Instance variables that are accessible are called exported instance variables. Exported instance variables can be inspected and–in some cases–assigned using the send operator. The instance variables of an object persist as long as the object it belongs to.

See Also: Classes, Objects

Messages :

A message is the way an object is requested to perform some action. Messages are sent to an object and composed of the object name, the send operator, and the selector name followed by arguments enclosed in parentheses. The selector has the same name as the method it is calling. Sending a message produces a return value, much like a function call with the return value varying depending on the operation performed.

See Also: Instance Variables, Methods, Objects

Methods :

A method is the operation performed in response to a message sent to an object.

See Also: Classes, Messages, Objects

Objects :

An object is an instance of a class. Each object has one or more attributes (called instance variables) and a series of operations (methods) that execute when a message is sent to the object. The object’s instance variables can only be accessed or assigned by sending messages to the object. Objects are created by calling a special function associated with a class.

See Also: Classes, Instance Variables, Messages, Methods

Self :

An object-oriented term describing a reference to the object that received the current message. In Clipper language, this reference is often the return value of a message send.

Send Operator :

A new operator (:) In Clipper language used to send messagesĀ to user interface objects.